SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Details 3) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Stock-Based Compensation
Stock-based compensation expense included in operating expenses	$ 886,000	$ 1,362,000	$ 2,234,000	$ 2,753,000
April 2013 Restructuring | One-time termination benefits
Stock-Based Compensation
Stock-based compensation expense related to extension of the post-termination exercise period	28,000
Research and development
Stock-Based Compensation
Stock-based compensation expense included in operating expenses	231,000	626,000	911,000	1,267,000
Restructuring charges
Stock-Based Compensation
Stock-based compensation expense included in operating expenses	28,000		28,000
General and administrative
Stock-Based Compensation
Stock-based compensation expense included in operating expenses	$ 627,000	$ 736,000	$ 1,295,000	$ 1,486,000